WINTERMUTE: Don't clean up _scripts mid-iteration

Scripts executing from ScEngine::tick() can call
ScEngine::unbreakableTick() via scCallMethod("SaveGame") and
applyEvent("BeforeSave").

This recursive execution could cause finished scripts being removed
from _scripts while ScEngine::tick() is still iterating over that array.
WINTERMUTE: Disambiguate empty and NULL strings when saving

The string stored is now strlen(s)+1, with length 0 indicating NULL.

Increment savegame version for this new format.

Old savegames are fixed by assuming VAL_STRING should never be NULL.
LASTEXPRESS: Fix uninitialized scalar field (CID1002847)
LASTEXPRESS: Fix unchecked return value in LastExpressEngine::pollEvents() (CID1004167)
LASTEXPRESS: Remove unneeded check for loaded sequence (CID1003911)

The sequence loading helper should already check if the sequence is loaded and clean up the instance if not
LASTEXPRESS: Fix unchecked return value (CID1003850)
LASTEXPRESS: Fix unchecked return value (CID1003854)
LASTEXPRESS: Fix uninitialized scalar field (CID1002849)
CREATE_PROJECT: Add extra configuration for compilation with LLVM
CREATE_PROJECT: Change PlatformToolset name for latest version of LLVM on Windows
TSAGE: Fixes and renaming for R2R rim scene
TSAGE: Fixes and renaming for R2R Rim lift exterior scene